1. Field of the Invention
This invention relates generally to road working or repair equipment and more particularly to a novel self-propelled road or pavement surfacing machine.
2. Prior Art
The road or pavement surfacing machine of the invention, hereinafter referred to simply as a road surfacing machine, is intended primarily for cutting or grinding concrete pavement to remove ruts, bumps, steps, and the like, and/or to cut anti-skid grooves into the pavement surface. For this reason, the invention will be described in this context.
Concrete roads or pavements are often resurfaced to restore pavements which have become degraded by extended usage, especially truck usage. Such degradation may take the form of ruts or the like which are worn into the pavement surface, undulations produced by bouncing of heavy vehicles, and steps resulting from relative vertical displacement or faulting of adjacent pavement slabs along their transverse joints. Pavement resurfacing may also involve cutting anti-skid grooves into the pavement surface.
At one time, the only way of resurfacing degraded pavements was to apply an overlay to the pavement surface. This overlay procedure, however, is time consuming, costly and causes extended interference with traffic. Pavement grooving was generally impractical.
For these reasons, machines were devised for resurfacing pavements by cutting or grinding the pavement surface. These road or pavement surfacing machines are designed to remove ruts, undulations, steps, and the like from a pavement by cutting or grinding the pavement surface and to cut anti-skid grooves into the surface. Examples of such machines are described in the following patents: U.S. Pat. Nos. 3,037,755; 3,409,330; 3,697,135; and 3,703,316.
One of the problems associated with such road surfacing machines involves their transportation to and from a work site and their propulsion during actual road surfacing operation. Thus, such a machine must be capable of transit to and from a work site along normal streets and highways and in normal street and highway traffic. On the other hand, the primary machine requirement for road surfacing operation is extremely high traction power at low speed.
Another problem associated with road surfacing machines of the class described is attaining adequate loading on the road surfacing means to achieve effective pavement surfacing action without excessive degradation of the cutters. Inadequate loading of pavement surfacing cutters, for example, allows the cutters to ride up or over the pavement which tends to glaze the cutters and create an uneven pavement surface. In the past, this problem was alleviated to some degree by using specially designed cutters for different pavement materials. This solution has not been satisfactory, however, owing to the difficulty and cost of providing and maintaining the required range of cutters and the difficulty of providing optimum cutter designs for all work conditions and pavement materials.
For this reason, ways were sought to increase the loading on the road surfacing cutters in order to force the latter to cut through rather than ride up or over the pavement. In some road surfacing machines this increase in cutter loading is accomplished by reacting downwardly on the cutters a portion of the weight of a tank containing water which is used to cool, flush, and lubricate the road surfacing cutters. U.S. Pat. No. 3,703,316, for example, discloses a road surfacing machine of this type. Even with such increased loading, however, it happens very frequently that the cutting resistance of the pavement and forward speed of the surfacing machine are such that the cutters still ride up and over the pavement.
In addition to glazing the surfacing cutters and producing an uneven surface, this riding of the cutters up and over the pavement has another serious consequence in existing road surfacing machines because of the manner in which their traction wheels are mounted. Thus, in the existing machines, when the cutting resistance of the pavement and forward speed of the surfacing machines are such that the pavement lifts the cutters up and over the pavement, there is exerted on the machines an upward force which opposes and reduces the contact pressure of their traction wheels with the pavement. This causes the traction wheels to spin and creates a highly undesirable surface defect in the pavement.